The battle between UPS and some of its pilots is getting more intense.

The union representing pilots for the logistics and shipping giant has opened a "strike center" near the company's Louisville, Kentucky air hub after long negotiations have failed to broker a deal.

"For five years, UPS has thumbed its nose at the negotiation process," President of the Independent Pilots Association (IPA) and UPS pilot Robert Travis said in a statement.

Mike Mangeot, a spokesperson for UPS, said that any request for a release from the negotiating table by the IPA is premature.

"UPS remains confident we will reach an agreement, just as we have in all past negotiations," Mangeot told Business Insider. "The recent activity is simply a publicity stunt, typical of past union tactics to try to pressure negotiations."

The largest sticking point between the two parties remains work rules that would limit pilot fatigue — though pay, healthcare, and retirement benefits remain in contention, the union said. The last successful negotiation occurred in 2006, and pilots continue to operate on those terms.

In 2013, a UPS cargo aircraft crashed short of a runway in Birmingham, Alabama, killing both crew members. The official NTSB report contributed the incident to multiple pilot errors, but also stated that the pilots were likely affected by fatigue.

Cargo pilots often receive higher compensation and lower flight hours per month than their airline counterparts, but they are excluded from FAA regulations that restrict the number of hours pilots can work at a given time.

While pilots that fly passengers are limited to nine hours of flying if any of that time is at night, cargo pilots can fly up to 16 hours, CBS news reported last year.

In October, the 2,500 represented UPS pilots voted almost unanimously to authorize a strike if negotiations fell apart, a potent message just before the industry's crucial holiday season.

UPS also called that event "a common union tactic in airline negotiations," the Wall Street Journal reported. Both parties returned to the negotiating table as scheduled that very month.

Negotiating contracts between a carrier and its pilots is commonly a lengthy process, often filled with posturing from both sides. Industry rival FedEx reached a six-year-deal with its pilots just last year after a similarly long negotiating period which began in 2011.

If the IPA does file a formal request for release from negotiations, authorities from the National Mediation Board must conclude that an impasse has in fact been reached. At that point a 30 day "cool-down period" is required before a strike or lockout is initiated, the IPA said.